What format videos are you playing?
For .mp4 .mkv and other HD formats I recommend SPlayer Portable: http://www.splayer.org/index.en.html
Important Note: Only use the Portable Edition, not installed. Also do not associate with video file types. It's better to put a shortcut to SPlayer in the SendTo Folder. Right click the video you want to play and select SPlayer from the SendTo Menu.
The reason for the note is some people, including myself, have noticed if you uninstall SPlayer and had file types associated, it could leave a "hole" in your file type associations. Other than that it's a nice player. Use Portable as noted and you should be ok.
One reason I recommend SPlayer is it will use GPU acceleration on some cards that other players won't. Or if the card has less memory than other players look for.
For more info please be more specific in detailing what you want to do.